and then the industrial revolution in the 18th century when you start harnessing all other kinds of energy. during that long block of time from a couple of million years ago until the industrial revolution, there was a point about 10,000 years ago when human beings began to farm, began to practice agriculture, and that harnessed a lot more energy than was possible by just hunting and gathering wild resources. keach: in the old world, we know that agriculture sparked the development of the world's first cities in places like sumer in ancient mesopotamia. but how did farming begin in the new world ? when scotty macneish first came to the tehuacan valley in 1962, he was seeking the answer to one simple question -- did agriculture evolve here or was it introduced from the old world ? then we'll measure out from the corners. keach: in a stratum of the purron cave that had been laid down thousands of years later than those in which he found the hunters and gatherers, macneish made a discovery that exceeded all expectations. macneish: this is a corn cob, and it's a real little one. keach: it may